The invention relates to a device for disinfecting water, comprising a gas discharge lamp including a discharge vessel with walls composed of a dielectric material, the outer surface of said walls being provided with at least a first and a second electrode, and the discharge vessel containing a xenon-containing gas filling.
By means of disinfection, pathogenic organisms such as bacteria, viruses, fungi and protozoa are rendered harmless. Both chemical and physical disinfection processes have been known for a long period of time. For the disinfection of water use is also made of chemical and physical processes. The chemical processes are largely based on the use of chlorine compounds and ozone. Physical processes, such as filtration, ultrasound, heating or irradiating with UV-light constitute a smaller burden for the ambient air. In addition, exposure of water to UV-radiation is a continuous and maintenance-free process.
It is known to use low-pressure or high-pressure mercury discharge lamps to disinfect water by means of UV-radiation, which discharge lamps emit very efficient UV-radiation having a wavelength of 254 nm and 185 nm.
However, mercury discharge lamps have certain drawbacks when they are used for the discontinuous treatment of small water quantities, for example at a tap. For example, when water is to be drawn, said discharge lamps are not directly operational. As they require a starter, their ignition is delayed by a few seconds. In addition, they do not reach their maximum capacity until after they have reached their operation temperature. Due to the low temperatures of tap water, the time necessary to reach the operating temperature is additionally increased. What is needed in fact is high-intensity UV-radiation which is directly available to avoid wasting water and energy.
The use of high-power radiators for ultraviolet light to disinfect water is disclosed already in EP 0 312 732, which high-power radiators comprise a discharge space filled with a filler gas, the walls of said discharge space being formed by a first and a second dielectric material, which is provided with first and second electrodes on the surface facing away from the discharge space, which high-power radiator also comprises an alternating current source which is connected to the first and the second electrodes and which serves to supply power to the discharge, both the dielectric materials and the first and second electrodes being transparent to said radiation. To change the spectral composition of the radiation, the composition of the filler gas is changed.
It is an object of the invention to provide a device for disinfecting water, which device comprises a gas discharge lamp including a discharge vessel with walls composed of a dielectric material, which are provided, at their outer surface, with at least a first and a second electrode, and which discharge vessel contains a gas filling containing xenon, the radiation of said gas discharge lamp having a spectral composition. which is optimally suited for disinfecting water.
In accordance with the invention, this object is achieved by a device for disinfecting water, comprising a gas discharge lamp including a discharge vessel with walls composed of a dielectric material, the outer surface of said walls being provided with at least a first and a second electrode, and the discharge vessel containing a xenon-containing gas filling, said walls being provided, at least on a part of the inner surface, with a coating containing a phosphor emitting in the UV-C range.
Such a water-disinfecting device is always 100% operational within milliseconds, and the spectral composition of its UV-radiation lies exclusively in the relevant range for disinfecting, i.e. between 230 and 300 nm. As a result, unnecessary heating of water or generating visible light is avoided. Since radiation of a wavelength below 230 nm is not generated, the formation of harmful nitrite is avoided. Such a device may have a service life of 20,000 operating hours.
Within the scope of the invention it is preferred that the phosphor comprises an activator selected from the group formed by Pb2+, Bi3+ and Pr3+ in a host lattice.
It may be preferred that the phosphor contains Pr3+ and lanthanum. These phosphors emit UV-C radiation in two bands in the 220 nm and 265 nm ranges. In these ranges, the maximum disinfecting effect of UV-radiation is obtained in accordance with DIN 503-10.UV-C radiation of these wavelengths is absorbed by the DNA-nucleotides of the micro-organisms, where it brings about a photodimerization and hence the destruction of the micro-organisms.
It may be preferred, that the phosphor contains Pr3+ and Ytrium. It is particularly preferred that the phosphor is selected from the group of LaPO4:Pr, LabO3:Pr, LaB3O6:Pr, YBO3:Pr and Y2SiO5. It can also be preferred that the phosphor is selected from the group of YPO4 and LuPO4:Bi.
The electrodes may be composed of a metal or an alloy reflecting UV-C light.
The invention also relates to a gas discharge lamp comprising a discharge vessel with walls composed of a dielectric material, the outer surfaces of said walls being provided with at least a first and a second electrode, and the discharge vessel being filled with a gas containing xenon, said walls being provided, at least on a part of their inner surface, with a coating containing a phosphor emitting in the UV-C range.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.